1. Field of the Invention
The present invention relates to aqueous dispersions of urethane-acrylic copolymers containing fluorinated acrylic monomers and to their use as finishing agents of textiles, leather and paper. The present invention particularly relates to the use of the dispersions in oil-repellent and water-repellent treatments.
2. Description of the Prior Art
Aqueous emulsions containing fluorocarbonic resins are widely used as finishing agents in the textile, leather and paper fields, because they impart good characteristics of oil- and water repellency to the substrates treated therewith. Many examples of aqueous emulsions containing fluorocarbonic resins, useful for the treatment of textiles, paper and leather, are described in the prior art literature.
By way of example, U.S. Pat. No. 5,164,252 (US1) describes hydrophobizing and oleophobizing compositions containing physical mixtures of a polymer containing perfluoroalkyl groups and of a cationically modified polyurethane dispersion, but it does not teach how to obtain a copolymer from the mixtures.
U.S. Pat. No. 5,346,949 (US2) describes aqueous emulsions containing fluorinated and non-fluorinated monomers mixed with a water soluble non-urethane cationic polymer which is able to increase the fixing properties of the resin on textiles. The water soluble cationic polymers used in US2 are expensive and not readily commercially available.
In U.S. Pat. No. 5,115,013 (US3), the preparation and the use in the finishing of natural or synthetic materials of aqueous dispersions of polyurethane-acrylate containing from 5 to 30 percent of fluorine, are described. The dispersions are obtained by grafting a mixture of acrylic monomers, some of which containing fluorine, onto non-functionalized cationic polyurethane dispersions.
In EP 98752 (EP1) a process for the preparation of stable aqueous dispersions of oligourethane-acrylate vinyl terminated containing hydrophilic ionizable groups, anionic or cationic, is described.
In EP 183119 (EP2) copolymers of xcex1,xcex2-ethylenically unsaturated monomers, modified with from 5 to 60 percent by weight, extremes included, of an oligourethane containing ionizable groups and xcex1,xcex2unsaturated terminal groups derived from acrylic and methacrylic monomers, are described. In EP2 neither the use of fluorinated monomers nor the use of the copolymers are cited in oil- and water repellent treatment. EP2 also describes the process for the preparation of the compounds. The EP2 process is not suited for the synthesis of the cationic perfluorinated urethane-acrylate copolymers of the present invention due to the poor emulsionability of the fluorinated monomers in the reaction medium.
On one aspect, the present invention is an aqueous dispersions of cationic urethane-acrylic copolymers containing fluorinated acrylic monomers characterized in that the dispersions are obtained by radical polymerization in aqueous dispersion of fluorinated and non-fluorinated acrylic monomers and of vinyl terminated polyurethane-acrylates containing cationic groups.
In another aspect, the present invention is a process for the radical polymerization in aqueous dispersion of mixtures of fluorinated and non-fluorinated acrylic monomers (A) on vinyl terminated polyurethane-acrylates containing cationic groups (B), characterized by preparing a pre-emulsion of (A) and of an aqueous dispersion of (B) by reducing the size of their particles to a value  less than 0.15 micron; by warming up the pre-emulsion to from 30xc2x0 to 100xc2x0 C. and by polymerizing by adding an initiator of radical polymerization.
According to the present invention, a group of fluorinated copolymers has been found, which is different in structure from the copolymers known for the same use and is prepared as a stable water dispersion. The water dispersion can be used as finishing agent in oil- and water-repellent treatment and is surprisingly effective even when used at low concentrations.
It is a main object of the present invention to provide aqueous dispersions of cationic urethane-acrylic copolymers containing fluorinated acrylic monomers obtained by radical polymerization in aqueous dispersion of fluorinated and non-fluorinated acrylic monomers (A) and of vinyl terminated polyurethane-acrylates containing cationic groups in aqueous dispersion (B). It has been found that the product obtained from the reaction of A with B give excellent oil and water repellent effects to the materials treated and finished with it, effects that are surprisingly much better than the ones obtained using A and B in physical mixture.
While not wishing to be bound by any particular theory as to the explanation of the reasons why the product obtained from the reaction of A with B exhibits a better performance in comparison with their physical mixtures, it is supposed that the fact that A and B are covalently bonded permits a better fixation of the active to textiles.
According to a fundamental aspect of the present invention, the amount of fluorinated acrylic monomer, which is the most expensive component of the mixtures normally used to obtain the expected effects, has been successfully decreased, while obtaining similar or better results in comparison with the ones obtained by the use of the separate components.
It is a further object of the present invention the procedure for obtaining the dispersions by radical polymerization of mixtures of fluorinated and non-fluorinated acrylic monomers, on vinyl terminated polyurethane-acrylates containing ionizable cationic groups.
It has now been found that the use of vinyl terminated urethane-acrylic copolymers as a base for the polymerization of fluorinated acrylic monomers permits a notable reduction of the amount of the surfactants that are normally used in polymerization or in the preparation of this kind of emulsions and that reduce the oil- and water repellent effects on textiles in the application step.
The vinyl terminated polyurethane-acrylates containing cationic groups in aqueous dispersion (B) can be obtained following the procedure described in EP 98752. According to EP 98752, aqueous dispersion of the vinyl terminated polyurethane-acrylates can be prepared by reacting, in a first step, an excess of an organic diisocyanate with a mixture of a diol containing ionizable groups and of an essentially linear macroglycol of the polyol-polyester type and/or polyol-polyether type having a molecular weight from 500 to 5,000 in order to obtain a prepolymer containing free isocyanate groups. The prepolymer is then converted into the vinyl terminated polyurethane-acrylate by reaction with a compound having hydroxyl groups able to react with isocyanic groups that has the following formula:
CH2xe2x95x90C(R)xe2x80x94COOX
where R is a methyl group or a hydrogen atom and X is a hydroxyalkyl group. The vinyl terminated polyurethane-acrylate is successively salified.
The preparation of the vinyl terminated cationic polyurethane-acrylate and its successive salification can be done using the same molar ratios described in EP 98752. The vinyl terminated polyurethane-acrylate thus obtained has a molecular weight from 2,000 to 50,000.
The utilizable organic diisocyanate of the present invention may be either of the aromatic, or of the aliphatic or of the cycloaliphatic type. Examples of suitable diisocyanates are 4,4xe2x80x2-dicyclohexyl-methanediisocyanate, 1-isocyanate-3-isocyanate-methyl-3,5,5-trimethyl-cyclohexane (or isophoronediisocyanate), 2,2,4-trimethyl-hexamethylene diisocyanate in admixture with the 2,6,4-trimethyl-hexamethylene diisocyanate isomer, 2,4- toluenediisocyanate either alone or in admixture with the 2,6-toluenediisocyanate isomer, and 4,4xe2x80x2-diphenyl-methanediisocyanate, or mixtures thereof.
As ionizable diols, the diols bearing tertiary amine groups, such as methyidiethanolamine, are particularly suitable according to the present invention. The utilizable macroglycols according to the present invention have a molecular weight from 500 to 5,000, preferably from 800 to 3,000, and are polyethers, polyesters or mixtures thereof.
Examples of utilizable polyesters according to the present invention are polyesters prepared by polycondensation of preferably aliphatic acids or anhydrides, having from 4 to 9 carbon atoms, with aliphatic diols having from 2 to 8 carbon atoms.
Examples of utilizable polyethers according to the present invention are the various types of polyethylene glycol, polypropylene glycol and, preferably, the polymerization products of tetrahydrofuran.
As compounds containing hydroxyl groups capable of reacting with the isocyanate groups particularly suitable according to the present invention are the following hydroxy-alkyl-acrylates or methacrylates: 2-hydroxyethyl-, 2-hydroxypropyl-, 3-hydroxypropyl- or 4-hydroxybutyl-acrylate or methacrylate, or mixture thereof.
For purposes of the present invention, the expression xe2x80x9cfluorinated and non-fluorinated acrylic monomersxe2x80x9d, means a mixture of from 40 to 70% by weight of fluorinated acrylic monomers and of from 30 to 60% by weight of non fluorinated acrylic monomers.
Fluorinated acrylic monomers utilizable according to the present invention have the following formula:
CnF2n+1CH2CH2OC(O)xe2x80x94C(R)xe2x95x90CH2
wherein R is a methyl group or a hydrogen atom, and n is a number equal or greater than 5, preferably from 5 to 12. Preferably, the fluorinated acrylic monomers utilizable according to the present invention are ethyl acrylates or methacrylates substituted in the 2 position of the ethyl radical by a perfluoropentylic, perfluorooctylic or perfluorododecylic radical, and mixtures thereof.
For the realization of the present invention, fluorinated monomers having the general formula
CnF2n+1SO2N(Rxe2x80x2)CH2CH2OC(O)xe2x80x94C(R)xe2x95x90CH2
can also be used wherein R and Rxe2x80x2 are an alkyl group or a hydrogen atom.
Examples of non-fluorinated acrylic monomers which can be used with the present invention include: butadiene; isoprene; chloroprene; styrene; xcex1-methylstyrene; p-methylstyrene; vinylic halogenides, e.g., vinyl chloride, vinylidene chloride, vinylidene fluoride; vinylic esters, e.g., vinyl acetate, vinyl propionate or vinyl stearate; esters of acrylic or methacrylic monomers, e.g., methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate or methacrylate, decyl acrylate, lauryl acrylate or methacrylate, stearyl methacrylate, N,N-dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate or glycidyl methacrylate; acrylamide, methacrylamide, N-methylolacrylamide, acrylonitrile, methacrylonitrile, N-substituted maleic imides, and mixtures thereof.
The ratio between the mixture of fluorinated and non-fluorinated acrylic monomers (A) and the vinyl terminated polyurethane-acrylate containing cationic groups (B) is such that in the resulting copolymer the amount of (B) is from 5 to 50% by weight.
The polymerization in aqueous dispersion of fluorinated and non-fluorinated acrylic monomers onto vinyl terminated polyurethane-acrylate containing cationic groups cannot be carried out with the known techniques of emulsion polymerization, by warming up under traditional stirring, in the presence of a surfactant and of an initiator of polymerization generating free radicals, due to the fact that it is difficult to emulsify the perfluorinated monomers and that the contact between the acrylic monomers and the vinyl terminated polyurethane-acrylate cannot therefore assure the growth of the acrylic chain on the urethane-acrylate. As a consequence, unstable emulsions are obtained by operating following the traditional method.
It has now been found that the polymerization can be carried out by previously preparing a pre-emulsion of the mixture of the fluorinated and non fluorinated acrylic monomers and of an aqueous dispersion containing the vinyl terminated polyurethane-acrylates.
In order to attain the aim of the present invention, it is necessary to prepare stable pre-emulsions by reducing the size of the particles to values lower than 0.15 microns, preferably lower than 0.10 microns.
After having prepared the pre-emulsion it is possible to carry out the polymerization by warming up the pre-emulsion and by adding a solution, or an aqueous dispersion, of a radical polymerization initiator into the pre-emulsion, under stirring. Useful radical polymerization initiators include organic azo-derivatives; organic hydroperoxides or peroxides, such as 2,2xe2x80x2-azobis-(2-methylpropionamidine) dihydrochloride, benzoyl peroxide, di-cumyl peroxide, terbutyl-hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide; and sodium, potassium or ammonium persulfate, used alone or together with a reducing agent such as sodium metabisulphite or sodium formaldehyde-sulfoxylate. The amount of initiator employable ranges from 0.01 to 1% by weight, preferably from 0.01 to 0.2% by weight, of the total weight of the monomers.
The polymerization temperature may vary from 30xc2x0 to 100xc2x0 C., depending on the kind of initiator. The preferred polymerization temperature range is from 40xc2x0 to 70xc2x0 C.
The solution containing the polymerization initiator is normally added over a period of one or two hours. Preferably, the reaction is maintained at a temperature in the preferred range until the residual content of acrylic monomers does not exceed 0.1% by weight of the initial amount of acrylic monomers.
Typically, the amount of urethane-acrylic copolymers in the aqueous dispersion useful for the realization of the present invention is from 20 to 30% by weight. This range of concentrations is particularly desirable because it allows for the production of concentrated dispersions while avoiding the transportation of large quantities of water and obtaining lower viscosities with resultant easier applications.
In the most common embodiment of the present invention, the reaction product of A and B is used in the form of an aqueous solution at a concentration of from 0.2 to 3% by weight in the composition used for finishing, preferably of from 0.5 to 2% by weight.